The invention relates to a method for arranging at least one through-channel in a solid body.
An example of a solid body of this type is a hot-runner, that is, a component for use in combination with an injection moulding device, which component comprises at least one channel for passage of heated plastic to the mould cavity of an injection moulding die. A single hot-runner comprises only one channel which is generally straight and which if required may possess a slightly tapering form. Such a channel can be obtained simply by drilling. For injection moulded products with a more complicated structure or for products which have to satisfy high quality control requirements, for instance compact discs, FLDs, NODs and other optical information carriers, the injection moulded product usually has to be manufactured via multiple gates. Use has to be made for this purpose of a hot-runner with one inlet opening which branches into a number of channels which each run out on the other side of the hot-runner. As will be apparent, these channels have to possess a form that is out of straight. In accordance with the known art, they are arranged in a block by way of a number of external bore machinings, followed where necessary by the re-filling of material portions where drilling out has been excessive.
The drawback of these steps is that the smoothness of the channels is difficult to control, that blind spots cannot be avoided when the heated plastic flows through the channels during an injection moulding process, and that the rheological characteristics of the channels generally leave something to be desired. This implies that the products obtained with the known art are capable of improvement.
The invention has for its object to offer a method of the type described can provide, which a considerable improvement in the quality of high grade injection moulded products. To this end the method comprises the following steps:
(1) providing at least two solid blocks which are together sufficiently large to form the body, PA1 (2) complementary modelling where required of corresponding side faces of the blocks, PA1 (3) forming a groove in each of the side faces, which pairs of grooves possess corresponding forms, PA1 (4) placing the noted side faces against each other such that the grooves together bound a channel, and PA1 (5) coupling the blocks into a body. PA1 (6) passing a liquid abrasive agent with force through the channel for a certain period of time in order to render the channel into a desired rheological form through honing, which honing may be pulsating. PA1 (7) manufacturing a number of bodies, each with a different time interval, PA1 (8) establishing which body has a channel complying best with the required rheological form, and PA1 (9) determining the noted time interval of that body. PA1 (10) dividing the body into blocks in lengthwise direction along a sectional plane of the channel and establishing the form of the thus formed grooves forming the channel in the original body. PA1 (11) successive accommodation of the hot-runners in the injection moulding device, PA1 (12) the manufacturing at least one injection moulded object, for example a compact disc, with each of these hot-runners, and PA1 (13) establishing with which hot-runner the best object has been manufactured.
This method is preferably succeeded by the following step:
Both blocks can be unified into a body by any desired technique. In the case of injection moulding devices however, very high pressures occur, so that joining by means of bolts for example cannot be considered. Recommended is the method whereby the blocks are unified into a body by vacuum soldering.
Of great importance in determining the required rheological form is the interval of time during which the liquid abrading agent has to be passed through in the so-called "slurry-honing". This can be effected by way of the following steps:
It should be understood that as a result of the passing of a liquid abrading agent through the body, a gradual abrasion of the wall of the or each channel occurs, whereby at a certain point in time the "ideal" rheological characteristics are obtained.
The above specified step (8) can now be performed by:
In the case where the body to be manufactured is a hot-runner, the above specified step (8) can be performed by:
For example, in the case of optical information carriers that are manufactured from high grade and very transparent plastic, establishing which of the objects produced is the best can be carried out by determining the optical properties, this being done at a number of places on the formed injection moulded product.
Finally, the invention relates to a solid body with at least one through-channel obtained by application of a method according to the invention of the type discussed above.